Ogham, the Celtic Tree Alphabet, was used in the Celtic lands and has been found on inscriptions dating from the 4th to the 6th century C.E. The alphabet and its use probably predates the found inscriptions and may date back to at least the 1st century C.E. because the written text use pre 4th Century grammatical elements. The existing inscriptions have, for the most part, been carved into stone. There is no reason to think that Ogham was not inscribed on wood, skin, or other materials as well. It’s just that stone endures the ravages of time better than softer, organic materials.
Ogham, is pronounced [ˈoːm] or [ˈoːəm] in Modern Irish and [ˈɔɣam] in Old Irish. Its origins are uncertain. According to one tradition it was a gift of the Irish god Ogma. Others attribute the name to the Irish phrase og-úaim (point-seam) which refers to the seam made by the point of a sharp weapon. Ogham is also known as or ogham craobh (tree ogham) beth luis fearn or beth luis nion, after the first few letters of the alphabet.
The following chart shows the tree ogham letters, with their corresponding names and trees, in vertical form, that is, for writing top-down in columns. The letters can be rotated 90 degree clockwise for horizontal writing.
For fun, here is a link to a transliteration tool. Ogham may have been used for divination, much as the Rune was and is used; and I find it much easier to learn than the more complex Tarot. Each letter of the Ogham alphabet corresponded to a specific tree, hence the tree alphabet name. Here are two links to web sites that provide the meanings of each of the trees in the Ogham alphabet: Site 1, Site 2.
If you feel attracted to the Ogham then you might create your own set of Ogham stick for divination. You can use a Sharpie and write each letter on a Popsicle stick, cut and carve small branches and inscribe a letter onto each stave (ask permission of each tree for a branch and give a small offering of cornmeal or tobacco in return) or even purchase a ready-made set on Etsy (search for Oghma Staves).
I'm Dr. Dave, a modern druid. I lived and worked in Bolivia and Peru for over six years, where I and was trained by Andean Shamans, and today practice modern druidism and contemporary shamanism.